In recent years, flat panel displays such as liquid crystal displays and plasma displays are being widely applied to various devices from mobile equipment such as portable telephones to large-scale devices such as public displays.
In this development of displays, emphasis has been placed on such factors as wide angle of field, high luminance, and high picture quality, and displays have been sought that provide superior display of images to users at any angle.
On the other hand, in the current state of ubiquitous computing that has come with the development of information equipment, the prevention of viewing by others of data of personal information or confidential information that is shown on displays has become an important problem.
In portable telephones of recent years, optical screens (louvers) have been provided to produce displays that allow viewing of display content only from a specific direction, but other people at locations substantially directly opposite the display such as directly behind the user are able to view the displayed data, rendering such displays inadequate from the standpoint of protecting confidentiality.
A picture display device has been proposed that allows viewing of a specific picture only by a viewer that is wearing viewing glasses having a picture-selection capability (refer to JP-A-S63-312788 (hereinbelow referred to as Patent Document 1)).
The picture display device disclosed in Patent Document 1 displays both pictures (hereinbelow referred to as private pictures) that can be viewed only by a user that is wearing viewing glasses having a picture-selection capability and other pictures (hereinbelow referred to as the public pictures) that can be viewed by a person not wearing these viewing glasses.
As shown in FIG. 1, the picture display device disclosed in Patent Document 1 is composed of picture information storage memory 402, synthesis circuit 405, saturation/brightness conversion circuit 406, picture display 408, viewing glasses-shutter timing generation circuit 409, and viewing glasses 411.
Based on frame signal 403, picture information storage memory 402 stores picture signal 401 that is received as input in frame units. The picture signal that is stored in picture information storage memory 402 is read two times at the frame period.
The picture signal that is read first is supplied to synthesis circuit 405 as first picture signal 404 that is compressed by one-half. The picture signal that is read second is supplied to synthesis circuit 405 as second picture signal 407 after undergoing a saturation and brightness conversion process by saturation/brightness conversion circuit 406.
The output of synthesis circuit 405 is supplied to picture display 408 as a display signal. Picture display 408 alternately displays a picture that is based on first picture signal 404 and a picture based on second picture signal 407.
Based on frame signal 403, viewing glasses-shutter timing generation circuit 409 generates viewing glasses-shutter drive signal 410 for driving a shutter that is equipped in viewing glasses 411. Viewing glasses-shutter drive signal 410 is a timing signal such that the shutter of viewing glasses 411 is ON (blocked state) in the interval in which a picture is displayed based on second picture signal 407. By driving the shutter of viewing glasses 411 based on viewing glasses-shutter drive signal 410 that is supplied as output from viewing glasses-shutter timing generation circuit 409, the user that is wearing viewing glasses 411 views only the pictures that are based on first picture signal 404.
A person other than the user who is not wearing viewing glasses 411 sees a gray picture in which the picture based on first picture signal 404 and the picture based on second picture signal 407 are merged due to the visual integral effect (afterimage) over time. This gray picture is a completely different picture from the picture based on first picture signal 404, and as a result, a person not wearing viewing glasses 411 is unable to view the picture that is based on first picture signal 404.